1. Field of the Invention
This invention relates to a semiconductor device, and more particularly relates to a semiconductor which has a compound semiconductor functional layer.
2. Description of the Related Art
A high electron mobility transistor (HEMT) is known as an electrical device which uses a gallium nitride (GaN) compound semiconductor. HEMT has a high electron (carrier) mobility rate and excellent high frequency properties. HEMT is comprised of a nitride semiconductor functional layer having a GaN layer which functions as a channel layer, and an aluminum nitride (AlGaN) layer which functions as a barrier layer stacked on this GaN layer by a hetero-junction. A two-dimensional electron gas channel (2DEG) in which high mobility electrons travel is produced close to the hetero-junction of the GaN layer. A source electrode and drain electrode are connected to the two-dimensional gas channel and a gate electrode is arranged between the source electrode and drain electrode. In a HEMT which has this type of structure, it is possible to realize a high carrier density via a piezoelectric field using spontaneous polarization and a lattice mismatch.
Furthermore, a HEMT is described in Laid Open Patent WO 03/071607 A1.
However, in the HEMT no concern was given to modulating the high carrier density or electric field within the two-dimensional electron gas channel in the channel direction, that is, carrier travel direction.